The present disclosure relates generally to pupillometry systems, methods, and devices. In particular, pupillometry systems and methods that automatically calculate a standardized output value that can be used by an operator for medical diagnosis are described.
Changes in the pupil can occur as a result of medications, drugs, and/or toxins (e.g., cough and cold medications, anticholinergic drugs, benzodiazepines, amphetamines, cocaine, lysergic acid diethylamide, marijuana, other narcotics, poisonous mushrooms, belladonna, chloroform, etc.). Pupil changes caused by medications, drugs and toxins are generally temporary. In addition to causing changes in size and response, drugs and/or toxins may affect a characteristic known as pupillary unrest, which is the variation in pupil size about its mean. Determining pupil size, pupillary unrest, pupillary response, and/or other pupillary characteristics can be useful in determining the presence and/or type of medications drugs, and/or toxins in the system of a patient. Further, changes in pupil size and unequal pupil size can be indicators of other serious conditions such as head trauma, brain tumors, and/or stroke. Thus, measuring pupil size and responses can be important for appropriate treatment for a patient.
Devices that measure the radius, diameter, circumference, or other characteristics of a pupil are generally referred to as pupillometers, and the analysis of these measurements is referred to as pupillometry. Pupillometry has a wide variety of applications. For example, precise measurements of pupil size may be useful in planning surgery or other procedures on the eye. Abnormal changes in pupil size, or failure of pupil size to change in response to stimuli (i.e., fixed pupils) may indicate that the patient has a neurological injury. Changes in the pupil size with time (i.e., pupillary unrest) can be correlated with drowsiness. It may additionally correlate with consumption of certain pharmaceuticals, and pupillary unrest may be useful in determining the activity of these pharmaceuticals.
Known pupillometers are not entirely satisfactory for the range of applications in which they are employed. For example, it can be difficult to assess pupillary unrest using only the data provided by a conventional pupillometer, which is typically reported as pupil diameter versus time. This can be difficult for several reasons. First, the amplitude of the variation is often quite small and difficult to appreciate, particularly when there are ongoing changes in the baseline pupil diameter, or noise in the system. Secondly, the operator may be unfamiliar with the frequencies generally associated with pupillary unrest, and may mistake variations in pupil size that are too high or too low in frequency to be clinically relevant with clinically important pupillary unrest. Lastly, the frequency of the pupil variation may change slightly during the measurement and confuse the operator.
In addition, known pupillometers report pupillometry data as size versus time, with no analysis of frequency components. This is only marginally useful if the user wishes to appreciate the frequency components of the pupillometry data. One technique for analyzing the frequency components is application of a Fourier transform. The Fourier transform changes data that is in the form of amplitude versus time to the form of amplitude versus frequency. A Fourier transform makes the amplitude of various frequency components apparent and can therefore be useful in interpreting pupillary unrest from pupillometry data. The Fourier transform is itself, however, difficult for an inexperienced operator to interpret. An inexperienced operator is unlikely to be aware of what frequency range is relevant to different clinical situations and/or how to correctly interpret frequency data.
Thus, there exists a need for pupillometry systems, methods, and devices that improve upon and advance the design of known pupillometers. Examples of new and useful pupillometry systems, methods, and devices relevant to the needs existing in the field are discussed below.
Disclosure addressing one or more of the identified existing needs is provided in the detailed description below. Examples of references relevant to pupillometers include U.S. Patent References: U.S. Pat. No. 3,782,364, U.S. Pat. No. 5,784,145, U.S. Pat. No. 7,625,087, and U.S. Pat. No. 8,127,882. The complete disclosures of the above patents are herein incorporated by reference for all purposes.